1. Field of the Invention
This invention relates to video amplifiers of the type employed to control the characters and background information on a cathode ray tube (CRT). More particularly, the present invention video amplifier relates to the independent control of the background intensity and the foreground intensity of the information on a cathode ray tube.
2. Description of the Prior Art
Heretofore, video display terminals and television sets were provided with contrast and brightness controls which are interactive. The contrast control adjusts the amplitude of the input signal to affect the intensity of the information being displayed. The brightness control adjusts the voltage level on the first control grid of the CRT to affect the luminous level of all information on the tube of the CRT. These prior art contrast and brightness controls are acceptable when embodied into standard television sets. Similarly, most prior art video display terminals (VDT's) do not illuminate the background. However, VDT's with ergonomic enhancements preferable have background illumination that is adjustable.
Heretofore, such illuminescent adjustment has been accomplished by the aforementioned brightness and contrast controls which by definition are interactive. It would be desirable to provide a video display terminal with ergonomic enhancements which permit independent adjustment of the intensity of the background information and the foreground information.